Dominic is a marathon runner. he admits that whenever he runs, he feels euphoric. he cannot begin his day without running for an hour. in the context of neurotransmitters, which of the following is most likely responsible for his feelings of pleasure from running?

a. the extended "high" from gaba reuptake
b. the compensatory effects of acetylcholine
c. the release of endorphins
d. the action of serotonin depletion during physical exertion